Watch Party feature is only available for the desktop version of Prime Video and is only supported on Chrome and Firefox.
Prime Video: Enjoy the film together thanks to Watch Party
Prime Video gets a major update on Fire TV and Android
Prime Video Watch Party: What it is and how to use it
extends Prime Video Watch Party support to Roku, smart TVs and consoles
expands Prime Video's Watch Party feature to Roku, smart TVs, and more - The Verge
Plans in the works for local professional sports on Prime - CBS Minnesota
9 Secret Prime Video Features You May Have Missed
Prime Video Watch Party Features Arrives on Roku, Smart TV — Here's How it Works
Twitch Now Lets Anyone Host Prime Video Watch Parties - IGN
How to Start an Prime Video Watch Party - Tech Advisor
How to Use Watch Party to Stream With Up to 100 People - The Plug - HelloTech